1. Field of the Invention
This invention relates to electronic integrated circuits, and in particular to improved binary decoders in integrated circuits.
2. Description of the Related Art
A binary decoder is a circuit that enables a single selected digital output from a defined set of digital outputs, based on an input binary value. The decoder produces an output signal on the single output that matches the input binary value. Binary decoders are essentially combinatorial logic circuits formed by an arrangement of logic gates. A binary decoder having an input value “n” bits is required to have “2n” outputs one of which corresponds with the n-bit value applied at the input. Binary decoders are widely used for performing selection functions where any single device or any single set of devices are required to be selected or enabled from a defined collection of devices or defined collection of device sets. A typical application is in selecting a row of memory cells in a memory device. Another typical application is in selecting a single IO device from a collection of IO devices in an electronic circuit.
A 2-to-4 decoder implementation according to the known art requires 16 transistors covering four different circuits, one for each combination of the input. At the same time each input signal is required to drive four GATE loads. Similarly, a 3-to-8 decoder requires as many as 32 transistors covering 8 different circuits, one for each combination of inputs, with each input having to drive 4 gate loads. This manner of implementation results in a bulky and expensive circuit requiring an undesirably large chip area. The capacitive loading on the input signals reduces the speed of the operation of the device.